Despite the the KB838306 Jet Hotfix not appearing in the list of fixes in SP1 KB article, it appears that the bug has been fixed. KB838306 updates msjtes40.dll to v4.0.8704.0 whereas a Windows 2003 Server with SP1 has v4.0.9025.0

The symptoms of the Jet bug include the appearance of a "hang", and increasing request queue count but static requests processed count (viewable in Performance Monitor). If you use IISState to dump the thread stacks you will see several deadlocked threads, such as the two below, which are waiting upon each other to give up a lock:

Thread ID: 27
System Thread ID: 120
Kernel Time: 0:0:0.78
User Time: 0:0:0.93
Other information: Thread is waiting for a lock to be released. Looking for lock owner.
Owning thread System ID: c64
Thread Type: Jet DB Query. Possible ASP Page
Executing Page: *****

# ChildEBP RetAddr
00 0a7fe1f4 77f43741 SharedUserData!SystemCallStub+0x4
01 0a7fe1f8 77f5d64e ntdll!ZwWaitForSingleObject+0xc
02 0a7fe234 77f42044 ntdll!RtlpWaitForCriticalSection+0x126
03 0a7fe23c 1b0058cc ntdll!RtlEnterCriticalSection+0x46
04 0a7fe2b8 03174602 msjet40!WZLocalTransporterID+0x24
05 00000001 00000000 oledb32!CDBInitialize::DoInitialize+0x32

--snipped--

Thread ID: 58
System Thread ID: c64
Kernel Time: 0:0:0.31
User Time: 0:0:0.109
Other information: Thread is waiting for a lock to be released. Looking for lock owner.
Owning thread System ID: 120
Thread Type: Jet DB Query. Possible ASP Page
Executing Page: *****

# ChildEBP RetAddr
00 0d5cdb08 77f43741 SharedUserData!SystemCallStub+0x4
01 0d5cdb0c 77f5d64e ntdll!ZwWaitForSingleObject+0xc
02 0d5cdb48 77f42044 ntdll!RtlpWaitForCriticalSection+0x126
03 0d5cdb50 1b812edc ntdll!RtlEnterCriticalSection+0x46
04 0d5cdb60 1b812ebc msjtes40!`string'+0x18
05 0d5cdb6c 1b8131ee msjtes40!`string'+0x24
06 0d5cdb90 7716fb13 msjtes40!`string'+0x2
07 0d5cdbb0 7716f9bf ole32!CreateInprocInstanceHelper+0x1a
08 0d5cdc8c 7716fa50 ole32!ICoCreateInstanceEx+0x89
09 0d5cdcb4 7716fa21 ole32!CComActivator::DoCreateInstance+0x26
0a 0d5cdcd8 7716fa90 ole32!CoCreateInstanceEx+0x21
0b 0d5cdd08 1b03ac4c ole32!CoCreateInstance+0x3a
0c a0007687 00000000 msjet40!ErrAllocateDbid+0x3c